1. Field of the Invention
The present invention relates to a signal processing apparatus and method for performing signal processing associated with quantization, on an input parameter, and to a signal coding apparatus and method in which the signal processing apparatus is used. Also, the present invention relates to a signal processing apparatus and method for inputting an index of a quantized output from quantization means and for performing signal processing associated with dequantization, and to a signal decoding apparatus and method in which the signal processing apparatus is used.
2. Description of the Related Art
Hitherto, various coding methods for performing signal compression by using statistical properties in a time domain and a frequency domain of audio signals (including voice signals and musical signals) and auditory characteristics of a human being are known. Broadly speaking, examples of these coding methods include coding in a time domain, coding in a frequency domain, and analysis-synthesis coding.
In transform coding in which coding is performed by performing an orthogonal transform on an input signal on a time axis into a signal on a frequency axis, the following has been proposed that, with a view to achieving a lower bit rate, dynamic bit allocation corresponding to an input signal is performed and quantization of coefficient data on a frequency axis is performed. However, the calculation of this bit allocation is complex, and in particular, when coefficient data on a frequency axis is divided in units of several pieces and vector quantization is performed by using the divided data as subvectors, if the bit allocation for each coefficient is changed, the calculation of bit allocation for quantization is complicated.
Furthermore, when bit allocation changes dramatically for each frame, which is a transform unit for the orthogonal transform, there is a drawback in that reproduced sound is likely to become unstable.
For this reason, the applicant of the present invention previously proposed in Japanese Unexamined Patent Application Publication No. 12-132194 (hereinafter referred to as xe2x80x9cthe conventional artxe2x80x9d), a signal coding apparatus and method, and a signal decoding apparatus and method, in which the calculations of bit allocation can be easily performed while dynamic bit allocation corresponding to an input signal is performed during the coding associated with the orthogonal transform, and in which reproduced sound does not become unstable even if bit allocation dramatically changes between frames.
In this conventional art, when coding is performed on an input signal on a time axis by using the orthogonal transform, a weight is computed according to the input signal, coefficient data obtained by being orthogonally transformed is assigned an order according to the order of this weight, and quantization with high accuracy is performed in accordance with this order. Therefore, even if bit allocation is performed dynamically according to the input signal, the calculation of the number of bits, which is assigned to each coefficient, can be performed simply.
Furthermore, by specifying parameters for calculating bit allocation in advance and by sending these parameters to a decoder side, it becomes unnecessary to send information of bit allocation to the decoder side, and thus the amount of additional information can be reduced, and a lower bit rate can be realized.
In the above-described conventional art, since there is a need that the results of a calculation of band-by-band bit allocation be completely the same between the coder and the decoder, the computation accuracy for this calculation needs to precisely agree between them.
However, for example, in a case where a signal coded by a coder which is implemented in a DSP (Digital Signal Processor) which performs fixed-point calculations is to be decoded by a decoder which is implemented in a personal computer, etc., if the decoder uses floating-point calculations, in spite of the fact that completely the same LSP (Line Spectrum Pair) codebook is referred to and the same codeword is input, a discrepancy in band-by-band bit allocation, resulting from computation errors, occurs between the coder and the decoder. Therefore, in this case, fixed-point calculations similar to those of a DSP need to be realized on a personal computer so that accuracy agrees to eliminate errors.
However, when computations to be performed by a fixed-point DSP having a general 40-bit accumulator is realized by a personal computer having a conventional 32-bit processor installed therein, a problem arises in that the number of computations becomes dramatically larger than when the same calculation is performed by floating-point calculation due to a limitation on the bit width of the processor.
The present invention has been proposed in view of the conventional situation. An object of the present invention is to provide a signal processing apparatus and method in which calculation results of band-by-band bit allocation are completely the same between a coder and a decoder, to provide a signal coding apparatus and method, and a signal decoding apparatus and method, in which the signal processing apparatus is used.
To achieve the above-mentioned object, in one aspect, the present invention provides a signal processing apparatus for performing signal processing associated with quantization on a first input parameter, the signal processing apparatus comprising: quantization means for quantizing the first parameter; and table referring means for preparing a table in which a result of a conversion of each representative value of a codebook is prestored and for determining a second parameter by referring to the table by using an index of a quantized output from the quantization means when the second parameter is to be determined on the basis of the first parameter quantized by the quantization means.
Such a signal processing apparatus prepares a table in which results of a conversion of each representative value of a codebook are prestored, and determines the second parameter by referring to the table using the index of the quantized output from the quantization means when a second parameter is determined on the basis of the first parameter quantized by the quantization means. Therefore, computations for parameter conversion do not need to be performed. Furthermore, since parameter conversion is also performed on the encoder side in a similar manner, a computation error between the encoder side and the decoder side can be prevented.
To achieve the above-mentioned object, in another aspect, the present invention provides a signal processing method for performing signal processing associated with quantization, on a first input parameter, the signal processing method comprising: a quantization step of quantizing the first parameter; and a table referring step of preparing a table in which a result of a conversion of each representative value of a codebook is prestored and determining a second parameter by referring to the table by using an index of a quantized output in the quantization step when the second parameter is to be determined on the basis of the first parameter quantized in the quantization step.
Such a signal processing method prepares a table in which a result of a conversion of each representative value of a codebook is prestored and determines a second parameter by referring to the table by using an index of a quantized output in the quantization step when the second parameter is to be determined on the basis of the first parameter quantized in the quantization step. Therefore, computations for parameter conversion do not need to be performed. Furthermore, since parameter conversion is also performed on the encoder side in a similar manner, a computation error between the encoder side and the decoder side can be prevented.
To achieve the above-mentioned object, in another aspect, the present invention provides a signal coding apparatus for performing coding by performing an orthogonal transform on a signal based on an input signal on a time axis and by performing bit allocation quantization on the obtained orthogonal transform coefficient, the signal coding apparatus comprising: orthogonal transform means for performing an orthogonal transform on a signal based on the input signal; parameter quantization means for quantizing a parameter based on the input signal; table referring means for preparing a table in which a result of a conversion of each representative value of a codebook is prestored and for determining bit allocation information by referring to the table by using an index of a quantized output from the quantization means when the bit allocation information is to be determined on the basis of the parameter quantized by the quantization means; and quantization means for performing bit allocation quantization on the orthogonal transform coefficient obtained by the orthogonal transform means on the basis of the bit allocation information determined by the table referring means.
Such a signal coding apparatus prepares a table in which a result of a conversion of each representative value of a codebook is prestored and determines bit allocation information by referring to the table by using an index of a quantized output from the quantization means when the bit allocation information is to be determined on the basis of the parameter quantized by the quantization means, and performs, in accordance with the bit allocation information, bit assignment quantization on the orthogonal transform coefficient obtained by performing an orthogonal transform on a signal based on the input signal. Therefore, computations for parameter conversion do not need to be performed. Furthermore, since parameter conversion is also performed on the encoder side in a similar manner, a computation error between the encoder side and the decoder side can be prevented.
To achieve the above-mentioned object, in another aspect, the present invention provides a signal coding method for performing coding by performing an orthogonal transform on a signal based on an input signal on a time axis and by performing bit allocation quantization on the obtained orthogonal transform coefficient, the signal coding method comprising: an orthogonal transform step of performing an orthogonal transform on a signal based on the input signal; a parameter quantization step of quantizing a parameter based on the input signal; a table referring step of preparing a table in which a result of a conversion of each representative value of a codebook is prestored and determining bit allocation information by referring to the table by using an index of a quantized output in the parameter quantization step when the bit allocation information is to be determined on the basis of the parameter quantized in the parameter quantization step; and a quantization step of performing bit allocation quantization on the orthogonal transform coefficient obtained in the orthogonal transform step on the basis of the bit allocation information determined in the table referring step.
Such a signal coding method prepares a table in which a result of a conversion of each representative value of a codebook is prestored and determines bit allocation information by referring to the table by using an index of a quantized output in the parameter quantization step when the bit allocation information is to be determined on the basis of the parameter quantized in the parameter quantization step, and performs bit allocation quantization on the orthogonal transform coefficient obtained by performing an orthogonal transform on a signal based on the input signal. Therefore, computations for parameter conversion do not need to be performed. Furthermore, since parameter conversion is also performed on the encoder side in a similar manner, a computation error between the encoder side and the decoder side can be prevented.
To achieve the above-mentioned object, in another aspect, the present invention provides a signal processing apparatus for inputting an index of a quantized output from the quantization means and for performing signal processing associated with dequantization, the signal processing apparatus comprising: dequantization means for dequantizing the index; and table referring means for preparing a table in which a result of a conversion of each representative value of a codebook is prestored and for creating a parameter by referring to the table by using the index.
Such a signal processing apparatus dequantizes an index of a quantized output, prepares a table in which a result of a conversion of each representative value of a codebook is prestored, and creates a parameter by referring to the table by using the index. Since parameter conversion is also performed on the encoder side in a similar manner, a computation error between the encoder side and the decoder side can be prevented.
To achieve the above-mentioned object, in another aspect, the present invention provides a signal processing method for inputting an index of a quantized output in quantization means and for performing signal processing associated with dequantization, the signal processing method comprising: a dequantization step of dequantizing the index; and a table referring step of preparing a table in which a result of a conversion of each representative value of a codebook is prestored and creating a parameter by referring to the table by using the index.
Such a signal processing method dequantizes an index of a quantized output, prepares a table in which a result of a conversion of each representative value of a codebook is prestored, and creates a parameter by referring to the table by using the index. Since parameter conversion is also performed on the encoder side in a similar manner, a computation error between the encoder side and the decoder side can be prevented.
To achieve the above-mentioned object, in another aspect, the present invention provides a signal decoding apparatus for inputting at least an index of a quantized output of a first parameter and a coded orthogonal transform coefficient from a signal coding apparatus which quantizes the first parameter based on the input signal and which performs bit allocation quantization on an orthogonal transform coefficient on the basis of the created bit allocation information by referring to a table in which a result of a conversion of each representative value of a codebook is prestored on the basis of the first quantized parameter when coding is to be performed by performing an orthogonal transform on the input signal on a time axis and by performing bit assignment quantization on the obtained orthogonal transform coefficient, the signal decoding apparatus comprising: table referring means for creating bit allocation information by referring to the table on the basis of the index; dequantization means for dequantizing the orthogonal transform coefficient on the basis of the bit allocation information created by the table referring means; and inverse orthogonal transform means for performing an inverse orthogonal transform on the orthogonal transform coefficient which is dequantized by the dequantization means.
Such a signal decoding apparatus inputs at least an index of a quantized output of a first parameter and a coded orthogonal transform coefficient from the signal coding apparatus, creates bit allocation information by referring to the table on the basis of the index, dequantizes the orthogonal transform coefficient on the basis of the created bit allocation information, and performs an inverse orthogonal transform on the dequantized orthogonal transform coefficient. Since bit allocation information is also created on the encoder side in a similar manner, a computation error between the encoder side and the decoder side can be prevented.
To achieve the above-mentioned object, in another aspect, the present invention provides a signal decoding method for inputting at least an index of a quantized output of a first parameter and a coded orthogonal transform coefficient from a signal coding apparatus which quantizes the first parameter based on the input signal and which performs bit allocation quantization on an orthogonal transform coefficient on the basis of the created bit allocation information by referring to a table in which a result of a conversion of each representative value of a codebook is prestored when coding is performed by performing an orthogonal transform on the input signal on a time axis and by performing bit allocation quantization on the obtained orthogonal transform coefficient, and for decoding the orthogonal transform coefficient on the basis of the index, the signal decoding method comprising: a table referring step of creating bit allocation information by referring to the table on the basis of the index; a dequantization step of dequantizing the orthogonal transform coefficient on the basis of the bit allocation information created in the table referring step; and an inverse orthogonal transform step of performing an inverse orthogonal transform on the orthogonal transform coefficient which is dequantized in the dequantization step.
Such a signal decoding method inputs at least an index of a quantized output of a first parameter and a coded orthogonal transform coefficient from the signal coding apparatus, creates bit allocation information by referring to the table on the basis of the index, dequantizes the orthogonal transform coefficient on the basis of the created bit allocation information, and performs an inverse orthogonal transform on the dequantized orthogonal transform coefficient. Since bit allocation information is also created on the encoder side in a similar manner, a computation error between the encoder side and the decoder side can be prevented.